Fixture

ABSTRACT

A fixture having an anchoring portion and an application portion intended for connection to a prosthesis. The application portion has an outer end and an end connected to the anchoring portion. The application portion includes a flared part whose outer dimensions widen from the end of that part connected to the anchoring portion in a direction toward the outer end of the application portion. This flared part is elastically resilient transversely to the longitudinal direction of the fixture.

FIELD OF INVENTION

The present invention relates to a so-called fixture which is anchoredto bone tissue. The fixture is of a kind that includes an anchoringportion with which the fixture is anchored, and an application portionintended for connection with a prosthesis and having an outer end and anend which is connected with the anchoring portion.

BACKGROUND OF THE INVENTION

Fixtures of this kind are used in prosthesis surgery, wherein theprosthesis, parts of a prosthesis, or a prosthesis holder is/areanchored in the bone tissue of a person with the aid of one or more suchfixtures. The fixtures may be used for different types of prosthesis andare of different sizes, said size depending on the type of prosthesisconcerned. However, the fixtures according to the present invention areprimarily intended for anchorage in tubular bone and may be used, forinstance, in the reconstruction of joints, such as finger joints and hipjoints. However, the invention is not restricted to these applicationsand may be applied to secure artificial limbs or other types ofprosthesis to the bone tissue of a patient.

The fixture includes an anchoring portion and an application portion.The anchoring portion is secured in the bone tissue of a patient, byscrewing said portion into a hole that has been predrilled in the bonetissue, for instance. The application portion is designed to enable itto be connected to prosthesis in a suitable fashion.

When the fixture anchoring hole is provided in the bone marrow in thelongitudinal direction of a bone, the mouth of the hole is likely to bewidened outwards due to the internal contour of the bone. Subsequent tohaving driven the fixture into said hole to the position intended, withthe anchoring portion fully screwed into the bone material, theapplication portion will be located in said widened region, eithercompletely or partially

This results in the formation of a space or clearing between the fixtureand the bone material. This is unsuitable both with respect to thestability of the anchorage and the healing process. It is thereforedesirable to avoid the occurrence of such a space.

Seen against this background, an object of the present invention is toprovide a fixture in which this drawback is eliminated, in other words afixture in which the occurrence of a space or clearing between thefixture and the bone tissue at the application portion of said fixtureis avoided.

SUMMARY OF THE INVENTION

This object is achieved in accordance with the invention by virtue ofthe application portion including a flared part whose outer dimensionswiden from the end of said part connected to the anchoring portion, in adirection towards the outer end of the application portion, wherein saidflared part is elastically resilient in a direction transversely to thelongitudinal direction of the fixture.

Because the application portion includes a part that widens in theaforesaid manner, the fixture will essentially fill out the space thatwould otherwise arise. Moreover, as a result of the elastic resiliencesaid flared part will adapt to the shape corresponded by the wideningoccurring at the outer end of the hole when anchoring the fixture. Thiseliminates the danger of healing problems caused by the presence of saidspace. Moreover, said part will be compressed and deformed as a resultof the widening at the mouth of the hole. Said part is therewithtightened against the flared surface and thus locked. This is achievedbecause the stresses generated tend to force said part to return to itsoriginal shape. The resilient part thus creates its own seating againstthe surrounding tissue, resulting in a highly stable anchorage.

According to one preferred embodiment of the invention, the flared partis formed by an outer wall that surrounds a cavity which is open towardsthe outer end of the application portion and which is provided withthrough-penetrating slots that extend from the outer end of theapplication portion, such as to connect the cavity with the outside ofthe outer wall. As a result of the slots, said outer wall forms a numberof tongue-like flaps whose free ends are able to spring inwards at theouter end of the application portion. The elastic resilience istherewith achieved in a constructively simple manner, wherewith theresilient part is well able to adapt to the shape of the widening at themouth of the insertion hole.

According to a further embodiment of the invention, the anchoringportion includes a threaded part which functions to enable the fixtureto be anchored by screwing the anchoring portion into the predrilledhole, said widening part having an outer contour which is rotationallysymmetrically about the centre axis defined by the threaded part.

Screwing of the anchoring portion into bone tissue is the most usualmethod of securing the fixture. Consequently, the inventive fixture isof significant interest since it is of the kind that can be screwed intobone tissue. Moreover, the inventive design of the application portionis particularly purposeful when anchoring the fixture by screwing thesame into bone tissue. Screwing of the fixture into bone tissue is alsofacilitated by the fact that the flared part, is rotationallysymmetrical.

According to a further embodiment of the invention, the flared part hasthe form of a truncated cone. Since the widening occurring at the mouthof the insertion hole is generally conical in shape, the truncated formof the flared part provides an advantageous adaptation to the widenedpart of said hole. The conical shape is also most suitable when thefixture is anchored by screwing the same into bone material.

According to another preferred embodiment of the invention, the coneangle is 5°-12°, preferably 7°-9°, The cone angle will preferably beslightly larger than the corresponding cone angle of the widening partat the mouth of the insertion hole. However, it should not be too large,since the occurring resistance to deformation may then be excessivelystrong and make anchoring of the fixture difficult to achieve and causeharmfully large stresses to build-up in the prosthesis anchoringconstruction. The chosen angular range of the cone angle is such as tooptimally balance these aspects in respect of the different applicationsthat may be of interest. For example, a fixture intended for a fingerjoint will preferably have a cone angle of about 8°, which is the mostpurposeful angle with respect to these aspects.

According to another preferred embodiment of the invention, each slotdefines an angle with the radial direction of the truncated cone. Thismeans that the slot walls will extend obliquely through the outer wallwhen seen in cross-section. It also means that each slot will extendobliquely in the axial direction, seen in the peripheral direction. Thisinclination of the slots means that the deformation occurring when theresilient part is compressed will be uniform, such as to essentiallyretain a conical shape when the fixture is screwed in.

According to another advantageous embodiment, the slots slope rearwardlyfrom within and outwards in relation to the direction in which thefixture is screwed in, this direction being defined by the threaded partof the anchoring portion.

Because the slots slope obliquely rearwards, the edge formed between thetrailing wall of the slot and the outside of the cone when screwing inthe fixture will be blunt, or obtuse, whereas the corresponding edge onthe leading wall of the slot will be sharp, or acute.

Because the edge that leads when screwing in the fixture is blunt, thereis less risk of said edge hooking fast into surrounding tissue materialwhen screwing in the fixture. This means that the compressivedeformation taking place when screwing in the fixture will not bedisturbed by said edge hooking into surrounding tissue material. Thedanger that hooking of the leading edge into surrounding tissue willcreate a resistance to screwing-in the fixture is similarly reduced. Thecone can be considered as being “stroked smoothly” by the surroundingtissue material when screwing in the fixture. On the other hand, theobliqueness of the cone has the reverse effect when unscrewing thefixture, since the slots then hamper unscrewing of the fixture. Thisreduces the danger of the fixture being unscrewed unintentionally,therewith making the anchorage more secure.

According to another preferred embodiment of the invention, the slotshave an angle of 20°-40° at their axially and radially outer ends. Thisangle will preferably lie in the range of 27°-33°, where an angle ofabout 30° is the most suitable in many applications. An angle in theaforesaid range will cause the desired deformation to be as uniform andas harmonious as possible, and allow optimum adaptation to the contourof the surrounding tissue material to be achieved.

According to another preferred embodiment, the outer wall has athickness of 0.3-1.0 mm, preferably a thickness of 0.5-0.7 mm.

The thickness of the outer wall will preferably be chosen so as tocreate a stable support against the surrounding tissue, on the one hand,and radial resilient compression of the parts situated between theslots, on the other hand. The aforesaid thickness range is believed toprovide an optimum balance in respect of these aspects.

According to a further preferred embodiment, the fixture is made oftitanium. Although the fixture can be made of some other suitablematerial, for instance polymeric material, composite material or othermetals than titanium, titanium is the material most preferred. Titaniumhas been found to adhere to bone material by so-called osseointegrationin the absence of those negative reactions that may often occur whenimplanting foreign material in body tissue. Titanium has the ability tointeract with and be integrated in bone tissue on a molecular level,such that the titanium will coalesce with the bone tissue. A titaniumfixture will therewith be anchored very securely.

The invention also relates to the use of the inventive fixture forsecuring a prosthesis in bone tissue.

The inventive use affords advantages of a kind corresponding to theadvantages given above with respect to the inventive fixture and itspreferred further embodiments.

The invention will now be described in more detail with reference to anadvantageous embodiment of the inventive fixture and with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinally sectioned view of a fixture constructed inaccordance with the invention.

FIG. 2 a is an end view similar to FIG. 2, with the direction of theslots reversed with respect to the direction of screwing-in rotation.

FIG. 3 illustrates schematically the principle according to which thefixture functions.

DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS

FIG. 1 is a longitudinal sectional view of an inventive fixture. Theillustrated fixture is intended for a finger joint and is dimensioned tothis end. The fixture comprises an anchoring portion 1 and anapplication portion 2. The anchoring portion has a length of about 20 mmand the application portion a length of about 10 mm.

The anchoring portion includes an external screw thread 3 which isadapted to enable the fixture to be screwed into a hole predrilled inbone tissue. In the illustrated case, the thread is an M6 thread. Thepredrilled hole will preferably have a diameter that is slightly smallerthan the inner diameter of the thread, i.e. a diameter of about 4.5 mm.The thread 3 extends along the full length of the anchoring portion 1.

Because the present invention is directed particularly to the design ofthe application portion 2, a detailed description of the design of theanchoring portion is believed to be unnecessary.

The application portion is comprised of a central body 4 which iscircular-cylindrical along the major part of its extension. It includesa central bore 5 that has a diameter of 2.5 mm. The outer end of thebody 4 has been given an hexagonal shape 6 (see FIG. 2) to enable theuse of a corresponding tool for screwing-in the fixture.

An outer wall 7 is arranged around the central body 4. This outer bodyhas the form of a truncated cone with the narrower end connected to theanchoring portion 1 of the fixture and the wider end connected to theouter end of the application portion, said truncated cone having roughlythe same length as the central body 4.

There is formed between the central body 4 and the conical outer wall 7a ring-shaped interspace that widens from the end adjacent the anchoringportion out towards the outer end of the application portion.

The outer wall has a thickness of 0.6 mm. The truncated cone has asmallest diameter of 5 mm, a largest diameter of 9 mm, and a length ofabout 10 mm. This corresponds to a cone angle of 8°.

As will be seen from FIG. 2, six slots 8 are provided in the conicalouter wall 7. Each slot is inclined in relation to the radial directionof the cone. The angle α between the radial direction and the slotdirection is 30° at the radially and axially outermost end of the slot.Each slot extends between both ends of the cone and is therewithorientated obliquely to the barrel surface of the cone in the axialdirection of said surface. Each slot has a width of 0.5 mm, i.e. adistance of 0.5 mm between two adjacent slot walls. The arrow A in FIG.2 indicates the direction in which the fixture is screwed in. Seen inthe direction in which the fixture is screwed in, the trailing slot wall9 forms a blunt edge with the outer side of the cone, wherewith theangle of said edge is about 120° at the large end of the cone. A sharpedge having an angle of 60° is formed at the leading slot wall 10 at acorresponding position.

The modus operandi of the invention will now be described in more detailwith reference to FIG. 3, which illustrates schematically and in sideview an inventive fixture during screwing of the fixture into bonematerial adjacent a finger joint.

In this case, the fixture is screwed into the marrow cavity in thelongitudinal direction of the bone. There is initially drilled in themarrow cavity a hole whose diameter corresponds approximately to theinner diameter of the thread. The fixture is self-tapping, so that thethread on the anchoring portion 1 will cut into the surrounding bonetissue and form a screw thread therein.

As will be seen from FIG. 3, the marrow cavity widens in a directiontowards the end of the bone. The marrow cavity will thus have agenerally conical extension at its mouth. The outer wall 7 on theapplication portion of the fixture has a cone angle which coincidesessentially with the widening of the marrow cavity. The fixture has notbeen screwed fully home in the FIG. 3 illustration. Continued screwingof the fixture into the bone from the position shown in the figure willcause the outer wall 7 to approach the wall defining the widening of themarrow cavity and ultimately lie in abutment therewith. When the fixtureis then screwed further into the bone, the conical outer wall 7 of theapplication portion will be compressed inwardly by the wall defining themarrow cavity, as indicated by the arrows B. This is made possible bythe fact that the outer wall 7 is resilient as a result of the slots 8,as described above. This compression can result in a reduction in thecone diameter at the large end of the cone from 9 mm to less than 8 mm.

When the fixture is screwed fully home, its outer wall 7 will thus lietightly against the conical expansion of the marrow cavity at the mouthof said cavity with a certain pressure. This eliminates the risk ofinflammation or the like in the space that would otherwise have beenformed in this region if the application portion of the fixture had hada typical cylindrical shape. The aforesaid abutment of the outer wall 7with the conically widening marrow cavity results in an effectivefixture support such as to provide a stable and secure fixture anchorageand also to increase its useful life.

FIG. 2 a shows the angle a reversed with respect to the direction ofrotation indicated by arrow B. Slots 15 slope forwardly in the directionof screwing-in rotation, so that sharp edges 16 can engage the sides ofthe hole in the bone, and oblique edges 17 do not so engage the bone.Bore 5 and hexagonal end 6 remain the same as in FIG. 2. The angle αbetween the radial direction and the slot direction is also about 30°,ranging between 20° and 40°, as is true of the equivalent slot angle inFIG. 2.

1. A fixture for anchorage in bone tissue, said fixture comprising: afixture anchoring portion and an application portion shaped andconfigured for connection with a prosthesis, said anchoring portionincluding a screw-threaded part, wherein the application portion has anouter end and an end connected with said anchoring portion, saidapplication portion being formed with a flared part whose outerdimensions widen from said end connected to said anchoring portion in adirection toward the outer end of said application portion, wherein saidflared part is elastically resilient transversely to the longitudinaldirection of said fixture; wherein said flared part has the form of atruncated cone and is formed by an outer wall that surrounds a cavitywhich is open toward the outer end of said application portion; whereinsaid outer wall is provided with through-penetrating slots which extendfrom said outer end of said application portion and which connect thecavity with the outside of said outer wall, wherein each said slotdefines an angle α with the radial direction of the truncated cone; andwherein said slots slope rearwardly from the cavity to the outside ofsaid outer wall in relation to the direction in which said fixture isrotated when screwing in said fixture, this direction being defined bysaid screw-threaded part.
 2. The fixture according to claim 1, whereinsaid screw-threaded part functions to anchor the fixture when screwedinto bone material and wherein said flared part has a rotationallysymmetrical outer contour around the center axis defined by saidscrew-threaded part.
 3. The fixture according to claim 1, wherein saidtruncated cone has a cone angle of 5°-12°.
 4. The fixture according toclaim 1, wherein said truncated cone has a cone angle of 7°-9°.
 5. Thefixture according to claim 1, wherein said slot angle α is 20°-40°, atthe axially and radially outer end of respective slots.
 6. The fixtureaccording to claim 1, wherein said slot angle α is 27°-33°, at theaxially and radially outer end of respective slots.
 7. The fixtureaccording to claim 1, wherein said outer wall has a thickness of 0.3-1.0mm.
 8. The fixture according to claim 1, wherein said outer wall has athickness of 0.5-0.7 mm.
 9. The fixture according to claim 1, whereinsaid fixture is made of titanium.
 10. A fixture for anchorage in bonetissue, said fixture comprising: a fixture anchoring portion and anapplication portion shaped and configured for connection with aprosthesis, said anchoring portion including a screw-threaded part,wherein the application portion has an outer end and an end connectedwith said anchoring portion, said application portion being formed witha flared part whose outer dimensions widen from said end connected tosaid anchoring portion in a direction toward the outer end of saidapplication portion, wherein said flared part is elastically resilienttransversely to the longitudinal direction of said fixture; wherein saidflared part has the form of a truncated cone having a cone angle of5°-12°, said flared part being formed by an outer wall that surrounds acavity which is open toward the outer end of said application portion;wherein said outer wall is provided with through-penetrating slots whichextend from said outer end of said application portion and which connectthe cavity with the outside of said outer wall, wherein each said slotdefines an angle α with the radial direction of the truncated cone; andwherein said slots slope rearwardly from the cavity to the outside ofsaid outer wall in relation to the direction in which said fixture isrotated when screwing in said fixture, this direction being defined bysaid screw-threaded part.
 11. A fixture for anchorage in bone tissue,said fixture comprising: a fixture anchoring portion and an applicationportion shaped and configured for connection with a prosthesis, saidanchoring portion including a screw-threaded part, wherein theapplication portion has an outer end and an end connected with saidanchoring portion, said application portion being formed with a flaredpart whose outer dimensions widen from said end connected to saidanchoring portion in a direction toward the outer end of saidapplication portion, wherein said flared part is elastically resilienttransversely to the longitudinal direction of said fixture; wherein saidflared part has the form of a truncated cone and is formed by an outerwall that surrounds a cavity which is open toward the outer end of saidapplication portion; wherein said outer wall is provided withthrough-penetrating slots which extend from said outer end of saidapplication portion and which connect the cavity with the outside ofsaid outer wall, wherein each said slot defines an angle α with theradial direction of the truncated cone; and wherein said slots slopeforwardly from the cavity to the outside of said outer wall in relationto the direction in which the fixture is turned when screwing in thefixture, said direction being defined by the screw-threaded part. 12.The fixture according to claim 11, wherein said slot angle α is 20°-40°,at the axially and radially outer end of respective slots.
 13. Thefixture according to claim 11, wherein said slot angle α is 27°-33°, atthe axially and radially outer end of respective slots.
 14. A fixturefor anchorage in bone tissue, said fixture comprising: a fixtureanchoring portion and an application portion shaped and configured forconnection with a prosthesis, said anchoring portion including ascrew-threaded part, wherein the application portion has an outer endand an end connected with said anchoring portion, said applicationportion being formed with a flared part whose outer dimensions widenfrom said end connected to said anchoring portion in a direction towardthe outer end of said application portion, wherein said flared part iselastically resilient transversely to the longitudinal direction of saidfixture; wherein said flared part has the form of a truncated cone andhaving a cone angle of 5°-12°, said flared part being formed by an outerwall that surrounds a cavity which is open toward the outer end of saidapplication portion; wherein said outer wall is provided withthrough-penetrating slots which extend from said outer end of saidapplication portion and which connect the cavity with the outside ofsaid outer wall, wherein each said slot defines an angle α with theradial direction of the truncated cone; and wherein said slots slopeforwardly from the cavity to the outside of said outer wall in relationto the direction in which the fixture is turned when screwing in thefixture, said direction being defined by the screw-threaded part.